1. Field of the Invention
The present disclosure relates to a random number generating device used in general random number applications such as a random number key and personal authentication.
2. Description of the Related Art
Conventionally, a method in which a physical thermal noise is used and a method in which an arithmetic random number is used are well known as the random number generating device.
For example, Japanese Patent Publication No. 4,625,936B proposes a random number generating device in which the physical thermal noise is used. FIG. 26 is a view illustrating an outline configuration of the conventional random number generating device in which the thermal noise is used, and FIG. 27 is a view illustrating a method for driving the random number generating device in FIG. 26. In the conventional random number generating device of FIG. 26, a set pulse current from set current setting unit 104 and a reset pulse current, which has a reversal polarity of the set pulse current, from reset unit 103 are alternately passed through magnetoresistive element 102 to change resistance of magnetoresistive element 102, thereby generating a random number. In the random number generating device of FIG. 26, a magnetization direction of a magnetization free layer in magnetoresistive element 102 is initialized by passing the reset pulse current. FIG. 28 is a view illustrating a method for controlling the random number generating device in FIG. 26. According to Japanese Patent Publication No. 4,625,936B, in the random number generating device of FIG. 26, after the magnetization direction is substantially aligned in one direction by passing the reset pulse current through magnetoresistive element 102, a pulse current (set pulse current) having a current value in which a cumulative magnetization reversal probability becomes 0.5 is added, whereby magnetoresistive element 102 can make the random number generating device in which both an event probability of a low-resistance state (an event corresponding to “0”) and an event probability of a high-resistance state (an event corresponding to “1”) become 0.5. In the random number generating device of FIG. 26, the current value in which the cumulative magnetization reversal probability becomes 0.5 is decided by previously measuring a characteristic in FIG. 28. At this point, because the magnetization reversal actually obtained in magnetoresistive element 102 varies due to the thermal noise, the random number can be obtained by detecting a change in the resistance state of magnetoresistive element 102.
On the other hand, Japanese Patent Publication No. 4,828,068B proposes a random number generating device in which the arithmetic random number is used. FIG. 29 is a view illustrating an outline configuration of the conventional random number generating device in which the arithmetic random number is used. The random number generating device in FIG. 29 is called a linear feedback shift register (LFSR) that is frequently used to generate the arithmetic random number. As illustrated in FIG. 29, the linear feedback shift register can generate the arithmetic random number with a simple circuit configuration. It is clear that a generation frequency of the arithmetic random number is unbiased (the event probabilities of 0 and 1 are substantially equal to each other).
The conventional random number generating devices each have the following problems. For example, in the random number generating device of Japanese Patent Publication No. 4,625,936B in which the physical thermal noise is used, magnetoresistive element 102 has temperature dependence, or a temporal change in the characteristic is generated, which results in a problem in that the generation frequency is biased. Actually, in the random number generating device of Japanese Patent Publication No. 4,625,936B, the random number generated by the magnetization reversal of magnetoresistive element 102 is input to integrator 106 through comparator 105, and output of integrator 106 is input to error amplifier 107, thereby adjusting the magnetization reversal probability. However, it is necessary to separately provide an adjustment circuit in order to obtain the configuration, which results in a problem in that the circuit is complicated. Additionally, the magnetization reversal probability is adjusted after the random number is generated, which results in a problem in that a bias still remains in a short term.
In the random number generating device of Japanese Patent Publication No. 4,828,068B in which the arithmetic random number is used, although the bias of the generation frequency is not generated, there is a problem in that the generated arithmetic random number sequence has a periodic characteristic. Due to the periodic characteristic, possibly decipher is easily completed in the case where the arithmetic random number sequence is directly used in cipher.